EP2577620B1 - Device for testing the authenticity of valuable documents - Google Patents

Description

The present invention relates to a method for checking the authenticity of a value document, to a corresponding apparatus for checking the authenticity of value documents and to a processing device for value documents.

So-called "compounded" counterfeits of value documents are composed of several parts, e.g. from one or more genuine document parts and / or one or more fake document parts. To detect such counterfeits, various methods are known, e.g. the evaluation of the reflection of the value document in order to detect adhesive strips or other connections of the individual document parts on the basis of reflection properties. However, this is not possible with all adhesive strips or connections, but only with those with recognizable deviating from the rest of the document reflection properties. Furthermore, fluorescence properties of a Composed counterfeiting can be used for recognition if the individual document parts are based on different (paper) substrates, or the position and / or orientation of optically recognizable features of a Composed counterfeit for the detection of optical breaks in the imprints of the forged value document serve. However, not all composite counterfeiting can be reliably detected by these methods.

Examples of such and similar methods are DE 10 2007015489 , of the WO 2008/149051 , of the WO 2009/133332 and the DE 10 2007019107 refer to.

The invention is therefore based on the object to provide a method by which Composed counterfeits can be detected as reliably as possible.

This object is solved by methods and devices having the features of the independent claims. In dependent claims advantageous embodiments and developments of the invention are given.

In a method for checking the authenticity of a value document, at least one intensity distribution of electromagnetic radiation passing through the value document is detected and evaluated. According to the invention, the at least one intensity distribution is detected spatially resolved in the dark field and from this a spatially resolved dark field characteristic is determined which, for example, can correspond to a digital intensity image of the value document in a desired spectral range.

Subsequently, suitable examination subareas of the value document are selected and in each case an individual characteristic intensity value is derived from the associated sections of the dark field characteristic, which is compared with at least one upper and / or lower threshold value. Depending on these comparisons, the examination subareas are assigned to one of several predefined suspiciouscy classes or classified with regard to the suspicion classes. From those examination subdomains that have been assigned to at least one particular suspicious class, for example a suspect class suggesting a forgery, a contextual area is formed by interconnecting the essentially contiguous examination subareas of the suspect class in question. In this case, substantially coherent examination sub-ranges mean that the examination sub-ranges are sufficiently close to one another, even if these are not directly adjoining pixels in the digital intensity image of the value document.

Furthermore, depending on the position of the context area within the value document, and possibly also depending on its shape, the value document is assigned to one of at least two predefined authenticity categories which is linked to that at least one specific suspect class to which the examination subareas forming the connection area are assigned were.

A device according to the invention for authenticating value documents accordingly comprises a detection device and an evaluation device for detecting and evaluating electromagnetic radiation passing through the value document. In this case, the detection device comprises a dark field transmission noise device, with which at least one intensity distribution of the electromagnetic radiation passing through the value document to be tested is detected spatially resolved in the dark field. The evaluation device then forms the spatially resolved dark field characteristic of the value document from the detected intensity distribution and assigns selected examination subareas of the value document to one of a plurality of predetermined suspect classes by means of the threshold comparison described above, forms a context area from the essentially contiguous examination subareas and finally arranges the value document depending on the situation , and possibly also on the shape, the context of a category of authenticity.

A processing device for value documents, in which a device according to the invention for authenticity testing is integrated, is in addition to Testing for authenticity preferably also designed to process value documents in such a way that the value documents are sorted according to the value document type and / or checked for their fitness for circulation.

Preferably, those examination subareas are combined to form a context area that has been assigned to a suspicious class that indicates a forgery of the value document. On the basis of this context area, the value document is assigned to a fake value document relating to the authenticity category, provided that the context area has a position typical within the value document for forged value documents.

The recognition of the counterfeit banknotes is therefore based on a two-stage recognition method, which determines in a first stage suspect examination sections of the value document and checks in a second stage, whether a coherent area formed from the suspect examination sections in terms of location to conclude a forgery.

In the dark field transmission measurement according to the invention, the radiation intensity of the radiation passing through the document of value to be tested is measured, but the proportion of the radiation which passes through the document of value essentially rectilinearly does not contribute or only to a negligible extent to the measurement result of the dark field transmission measurement. Rather, essentially only the strongly deflected radiation in its propagation direction contributes to the measurement result of the dark field transmission. For this reason, call in a dark field transmission measurement and subregions and especially dividing lines one Composed counterfeiting particularly striking measurement results, which would not be recognizable, for example by means of a bright field transmission measurement, is measured in the above all rectilinear or at least substantially straight through the document of value passing radiation.

Compared to the bright field transmission measurement, the use of the dark field transmission measurement is of great advantage, since the dark field transmission measurement provides particularly meaningful digital intensity images as a basis for the further process. In this case, in particular to the e.g. With an adhesive separating lines between two document parts or on the adhesive strips or other adhesive bonds applied there, an intensity profile of scattered (i.e., dark field) radiation which is significantly different from that within the document parts of a Composed counterfeit. The (scattered) radiation measured in the dark field thereby assumes a different intensity profile than in the bright field, because the ratio between linear transmission and scattering in the case of an adhesive or adhesive strip is generally a completely different one than in the case of the document parts themselves.

It is an essential advantage of the invention that, with the location of the transition region in the evaluation of the dark field characteristic, a morphological criterion is taken into account which allows a global assessment of the relevant value document. The marked intensity variations at the separating lines measured in the dark field transmission make possible particularly reliable and stable results of the described detection method.

The selected examination subareas of the value document may, for example, be subareas of the value document that consist of individual documents Pixels, pixel groups or larger areas of the dark field pattern. When assigning the selected examination subareas of the value document to one or more suspected classes, a characteristic intensity value of the dark field characteristic of the respective examination subarea is compared with the upper and / or lower threshold value. In this case, the characteristic intensity value of the relevant dark field characteristic can be, for example, an average value or median value of the individual intensity values. If the dark-field characteristic comprises only one pixel, its intensity value can be used as a characteristic intensity value of the dark-field characteristic. The comparison of the characteristic intensity value with the threshold is preferably a greater-no-comparison. The suspect classes may relate to graduated probabilities of being counterfeit, eg, "most likely falsified", "presumably counterfeited", "unknown", "presumably genuine", "most likely genuine", or the like.

In order to form the connected areas, criteria are specified with regard to those suspected classes from which examination subareas enter into the context area and when these are regarded as substantially coherent. For example, the area of interrelations can be formed from adjacent examination subsections of the suspected classes "most likely fake" and "presumably counterfeit".

The term electromagnetic radiation in the present case comprises light in the visible spectral range or radiation in the infrared range or in the ultraviolet range. Accordingly, the intensity distribution of the value document to be tested in the infrared range, in the visible spectral range or detected in the ultraviolet range, wherein also any combinations of these three spectral ranges are conceivable. For example, particularly good recognition results can be achieved by detecting intensity distributions in the infrared range and / or in the green visible spectral range. In this case, the intensity of the scattering of the electromagnetic radiation caused by the material of an adhesive, adhesive tape or other adhesive bond depends on its wavelength. As a rule, there is an optimal spectral range, which provides particularly clear results in the dividing lines of Composed counterfeiting by means of dark field transmission measurement. This optimal spectral range can be determined experimentally or by means of numerical simulation calculations.

According to a preferred embodiment, an intensity distribution is detected in each case in a plurality of spectral regions, and the spatially resolved dark field characteristic is determined from the detected intensity distributions by linking spatially corresponding values of the intensity distributions of different spectral ranges. In this case, in particular, a weighted, location-dependent linkage has proved to be advantageous, ie a link in which the intensity values of different spectral regions are provided with weighting factors and suitably linked to one another, eg, additive or multiplicative. Other links, such as subtractive or divisive links, may also be eligible, depending on the particular Composed counterfeit and the spectral ranges selected. It has been found that it is particularly advantageous for the reliable detection of parting lines to detect respectively an intensity distribution in the infrared range and in the green visible spectral range in order to derive the spatially resolved dark field characteristic by local (possibly weighted) averaging of the two intensity distributions to determine. In the simplest case, however, the dark field characteristic is equal to the spatially resolved intensity distribution of the electromagnetic radiation of a single spectral range.

The selected examination subareas of the value document can be assigned to a suspicion class as a function of local and / or global threshold values. It is thus also possible to use threshold values that are valid only for specific, local areas of the value document to be checked, e.g. Local threshold values are preferably used when the dark field transmission of an uncorrected value document assumes locally strongly varying intensity values (e.g., by security elements, imprints, or the like).

The threshold values are preferably defined or derived as a function of one or more reference subareas of the value document. Alternatively or additionally, the thresholds may also be derived from predetermined standard thresholds, which may be e.g. determined by a variety of forged default documents.

The reference subareas from which local or global threshold values are derived can be any subareas of the value document to be tested which are as safe as possible without dividing a parting line, so that suitable threshold values can be determined against which the intensity values of a parting line are conspicuous - or subliminal. In particular, in the case of the reference subregions analogous to the test subareas described above, individual pixels, a group of adjacent pixels or larger area raster regions of the pixels may be used Dark field characteristic act. Preferably, the reference subareas from which local thresholds are derived and the test subareas that are tested against the local thresholds are only slightly spaced.

To set the threshold values, characteristic intensity values of the dark field characteristics of different reference subregions of the value document are preferably arithmetically linked with one another. The characteristic intensity values of the dark field characteristics of the reference subregions can be determined analogously to the characteristic intensity values of the test subareas. These characteristic values of the various reference portions may then be arithmetically linked (e.g., as an average, median, or the like) to derive therefrom the thresholds needed.

According to another embodiment, the thresholds are set by correcting or adjusting default thresholds of a standard value document. In this case, a standard threshold value for forming a threshold applicable to the present value document is corrected upward if a characteristic intensity value derived from the dark field characteristics of different reference subregions is above a standard intensity of the standard value document. Accordingly, a default threshold value is corrected down if the characteristic intensity value derived from the dark field characteristics of different reference portions is below a standard intensity of the standard value document. In this way, standard threshold values can be adapted to the actual dark field transmission of a value document, which in particular can depend strongly on its state of use. At least one of the suspected classes is a suspected class suggesting a forgery of the value document. Accordingly, test sections whose characteristic intensity value is above an upper threshold or below a lower threshold are assigned to this suspicion class. From these parts of the examination, the connection area is finally formed.

In this case, the threshold values are preferably selected such that, on the one hand, the partial intensity characteristic of the respective dark field characteristic lies above the aforementioned upper threshold value or below the lower threshold value mentioned above, and on the other hand, in the case of partial examination sections which are in the range the sub-documents or their substrates lie, the characteristic intensity value of the respective dark field characteristic is between the upper and lower threshold. The first-mentioned parts of the examination are then assigned to a suspected class, which indicates a forgery, while the latter are assigned to a suspected class, which indicates an unaltered, genuine document of value. If further classified suspect classes exist with regard to the probability of counterfeiting, corresponding further threshold values are needed to define these suspect classes.

In this case, at least one examination subarea is selected on an edge of the value document or on an edge of a (previously detected or known) security element of the value document which was previously assigned to a suspicious class indicating a forgery. Then, on the basis of this examination subarea, further test subareas which are substantially related to it are also determined, which likewise include a suspicion class pointing to a forgery are assigned. Finally, all examination subareas determined in this way are combined to form a context area in order to assign the value document to a category of authenticity as a function of the form and / or position of the contextual area.

According to the invention, therefore, the fact is exploited that Composed counterfeits have typical dividing lines between two edge regions of the value document or enclose a security element. To detect them, the described step-by-step approach is advantageous in that not all, or at least a large number of test sections must be assigned to a suspect class, but only tested on the basis of an examination section pointing to a forgery at the edge of the document with this contiguous examination sections. In this way, a dividing line running from edge to edge or enclosing a security element can be reconstructed step by step.

Accordingly, according to the invention, in the evaluation of the position of the stepwise determined context area, it is checked whether it extends from one side of the value document to the same side or to another side or encloses a security element. A value document with such a context area is then assigned to the authenticity category "forgery". In addition to the location of the context area, the form of the context area can additionally take into account the number of examination subareas which have been assigned to a suspicious class indicating a forgery.

Preferably, a plurality of suspicion classes suggesting a forgery are predefined, eg graduated according to forgery probabilities of the Test sections. The classification of the value document into a category of authenticity can then take place in such a way that examination subareas assigned to a suspected class, which with a high probability of a forgery, strongly influence this classification.

Figur 1

eine Vorrichtung zur Echtheitsprüfung von Banknoten;

Figur 2a

ein Beispiel einer Composed-Fälschung einer Banknote;

Figur 2b

das Intensitätsprofil einer Dunkelfeldtransmission entlang einer Linie durch die Composed-Fälschung der Figur 2a;

Figuren 3a bis 3f

beispielhafte Querschnitte durch Composed-Fälschungen, welche typische Formen von Trennlinien zwischen den Dokumentteilen von Composed-Fälschungen zeigen;

Figur 4

ein Ablaufdiagramm eines Verfahrens zum Detektieren von Composed-Fälschungen;

Figur 5

ein Histogramm zur Bestimmung von Schwellenwerten;

Figuren 6a bis 6c

beispielhafte Verläufe von Trennlinien von Composed-Fälschungen; und

Figur 7

ausgewählte Prüfungsteilbereiche gemäß einer besonderen Ausführungsform des Verfahrens der Figur 4.

Further features and advantages of the invention will become apparent from the following description of the embodiments according to the invention and further alternative embodiments in conjunction with the drawings, which show:

FIG. 1

a device for checking the authenticity of banknotes;

FIG. 2a

an example of a composed counterfeit of a bill;

FIG. 2b

the intensity profile of a dark field transmission along a line through the Composed counterfeit FIG. 2a ;

FIGS. 3a to 3f

exemplary cross-sections of composed counterfeits showing typical forms of dividing lines between the document parts of composed counterfeits;

FIG. 4

a flowchart of a method for detecting Composed counterfeits;

FIG. 5

a histogram for determining thresholds;

FIGS. 6a to 6c

exemplary gradients of dividing lines of Composed counterfeits; and

FIG. 7

selected examination sections according to a particular embodiment of the method of FIG. 4 ,

The embodiments of the invention described below relate to the recognition of Composed counterfeits of banknotes, ie the assignment of a banknote, which was composed of genuine and / or counterfeit banknote parts, to a authenticity category "forgery" or "Composed forgery". In addition to banknotes, the method of course for any other value documents can be used, for. As badges, official documents, shares, debentures or the like.

FIG. 1 schematically shows a device 1 for checking the authenticity of banknotes BN. In this case collimated by 3 collimated electromagnetic radiation 2 strikes the banknote BN. The electromagnetic radiation 7 passing through the banknote BN in a direction different from the direction of the incident electromagnetic radiation 2 is measured in the dark field by means of suitable imaging optics 4, 5, which in the present case comprises a lens 4 and a diaphragm 5, and a dark field transmission measuring device 6. The dark field transmission measuring device 6 can be, for example, any suitable detector, for example a camera, a line scan camera, a CCD sensor or the like.

The incident electromagnetic radiation 2 is, in particular, white or colored light in the visible spectral range, UV radiation in the ultraviolet spectral range or IR radiation in the infrared spectral range or combinations of these or other spectral ranges.

According to Fig.1 incident the incident electromagnetic radiation 2 obliquely to the normal of the banknote surface on the banknote BN and is detected as passing radiation 7 in the direction of these normals, ie with a suitable angular deviation from the angle at which the electromagnetic radiation 2 impinges on the banknote BN. Likewise, the electromagnetic radiation 2 can strike the banknote BN in the normal direction (ie perpendicularly) and the passing radiation 7 can be detected in a direction different from the normal (ie obliquely to the banknote BN). It is also possible that the electromagnetic radiation 2 impinges on the banknote BN obliquely to the normal and the passing radiation 7 is detected in a direction which is different from the normal and from the angle in which the electromagnetic radiation 2 is applied to the banknote BN hits. All these variants are to be understood here as "dark field transmission measurement".

The dark field transmission measuring device 6 detects radiation 7 passing through the banknote BN at an angle which is sufficiently different from the angle at which the radiation 2 'extends substantially rectilinearly through the banknote BN. In principle, however, it is sufficient for a dark field transmission measurement according to the present invention if a still detected portion of the rectilinear radiation 2 'is so strongly attenuated that it contributes only insignificantly to the measurement result compared to the detected scattered radiation 7.

The dark field transmission measuring device 6 is connected by a data line 8 to a measuring device 9 and together with it forms a detection device 10 which detects the electromagnetic radiation 7 passing through the banknote BN in a spatially resolved manner in the dark field, ie as Rasterized or pixel-based digital image. About the measuring device 9, the detection device 10 is connected via a further data line 8 with an evaluation device 11, for example with a personal computer with a suitable evaluation software that evaluates the detected radiation 7 and the banknote BN finally one of at least two predetermined authenticity categories (eg "real" or "fake / suspect").

The authenticity checking device 1 can in turn be part of a banknote processing device (not shown), which performs any further processing of the checked banknote BN. From this, the banknotes BN, e.g. counted, stacked, sorted according to any criteria or checked for fitness for circulation. The banknote processing device comprising the authentication device 1 according to the invention may be a banknote processing device which reissues banknotes after their processing. However, the invention also encompasses a banknote processing device with the authenticity checking device 1 according to the invention, which can receive and store banknotes BN to be deposited and / or issue banknotes BN to be paid out.

FIG. 2a shows a Composed counterfeiting of a banknote BN, which consists of a counterfeit banknote part 21 and a genuine banknote part 22. The banknote parts 21, 22 are connected to an adhesive in the region of the dividing line 23 between the banknote parts 21, 22. The adhesive can z. B. applied in liquid form and then cured and is usually transparent. In principle, Composed banknotes BN can be composed of counterfeit banknote parts 21 and / or genuine banknote parts 22 in any desired manner. In particular, composed banknotes BN can also be composed of more than two banknote parts. The composed banknote BN the Fig. 2a is with a denomination statement 26 and provided with a security feature 25. Additional security features, such as watermarks, security threads or the like, may additionally be present.

FIG. 2b shows the profile profile 31 of the intensity A of the dark field transmission by the Composed banknote BN of Fig. 2a along the dashed line 30. In the region of the provided with an adhesive dividing line 23, a clear intensity maximum 31a can be seen, which can be distinguished on the basis of a threshold value 32 of other, eg noise-induced intensity fluctuations of the dark field transmission. The maximum 31a results from the fact that the adhesive along the parting line 23 diffuses the incident electromagnetic radiation 2 substantially more strongly than the (paper) substrate from which the banknote parts 21, 22 are made. This effect is particularly good in the dark field to recognize, for example, in the Fig. 3 exemplarily sketched variants of Composed counterfeits. In the FIGS. 3a to 3c the banknote parts 21, 22 of the Composed banknote BN are glued together with an adhesive, whereas in the Figures 3d to 3f in the region of the parting line 23, an adhesive tape 24 is applied, which connects the banknote parts 21, 22.

As a result of gluing a Composed banknote BN by means of an adhesive, a gap filled with adhesive between the banknote parts 21, 22 can arise in the area 28a ( Fig. 3a ). If the edges of the banknote parts 21, 22 touch ( Fig. 3b ), however, due to the generally uneven course of these edges, there is an adhesive area 28b filled with adhesive. Both at the in Fig. 3a as well as in the Fig. 3b As shown, the adhesive areas 28a, 28b can not be seen in a bright field transmission image. This is the case when the intensity measured in a bright field transmission measurement is in the adhesive areas 28a, 28b does not change significantly. However, since the ratio between scattering and absorption is completely different for an adhesive than for homogeneous banknote paper, the dividing lines 23 can be easily recognized by means of a dark field transmission measurement on the basis of the scattering significantly changing in the regions 28a, 28b.

By analogy with this, when glued together with an adhesive tape or tape 24 (eg with a transparent adhesive strip), as shown in FIGS Fig. 3d and 3e represented, between the banknote parts 21, 22 form gaps areas 28d, 28e, which may possibly even be detected together with the adhesive tape 24 on the basis of the significant scattering by means of a dark field transmission measurement. At the in Fig. 3c and 3f Composed banknotes BN shown in cross-section overlap the banknote parts 21, 22. These overlapping areas are also well recognized on the basis of the significant scattering by means of a dark-field transmission measurement. In addition, an adhesive tape 24 projecting beyond the edge of the composed banknote BN is also detected on the basis of a significantly higher scattering by means of a dark-field transmission measurement.

In all the examples presented above, the exact course of the dark field transmission in the region of the dividing line 23 or the adhesive tape 24 depends on various factors, in particular on the frequency range of the irradiated electromagnetic radiation 2, on the material of the adhesive or adhesive tape 24 used and on the material (eg Banknote paper) of the banknote parts 21, 22. In dividing lines 23 according to the in the Fig. 3a, 3b, 3d, 3e variants shown is compared with the banknote parts 21, 22 regularly detect an increased dark field transmission. Of course it could be in the area of the dividing lines 23 of the Fig. 3a, 3b, 3d, 3e also come to a relatively reduced dark field transmission, eg in unusual banknote materials, such as plastic substrates, or the like. Accordingly, in the overlapping areas of the parting lines 23 of FIG Fig. 3c and 3f usually found a reduced dark field transmission. In any case, the expected intensity profile of the dark field transmission can be determined experimentally or by means of simulation calculations.

Fig. 4 schematically shows the steps of a method for detecting Composed banknotes BN, which in the following in connection with the Fig. 5 to 7 is explained.

In the method according to Fig. 4 is in a first method step S1 with the previously in connection with Fig. 1 Detection device 10 recorded the dark field transmission of a banknote BN spatially resolved. In this case, intensity values A of the dark field transmission are spatially resolved, ie spatially scanned or spatially scanned, determined for different spectral ranges. Subsequently, the detected dark field transmission in the method steps S2 to S6 is evaluated by means of the evaluation device 11. In method step S2, the intensity values A of the dark field transmission registered spatially resolved for at least two different spectral ranges (eg for the spectral regions "green" and "infrared") are linked pointwise (eg added or multiplied) in a location-dependent manner in order to determine a spatially resolved dark field characteristic C of the banknote BN , Of course, it is possible to detect the intensity values A of the dark field transmission spatially resolved only for one spectral range and to use them as a dark field characteristic C, whereby the linking of the intensity values A detected spatially resolved for different spectral ranges would be omitted in method step S2. Alternatively or additionally, to determine the dark field characteristic C, the intensity values A of the dark field transmission Also be associated with equally spatially resolved values of a bright field transmission, a reflection or other measure. In this context, it is also conceivable to use supplementary ultrasonic transmission measurements in order, for example, to be able to detect adhesive tape 24 particularly well in the area of a security thread. In addition, it is conceivable to detect fluorescent light emitted under UV illumination by means of a fluorescence sensor.

Since significant banknote-dependent variations of the average darkfield characteristic are to be observed, the darkfield characteristic C of the banknote BN depends strongly on its use state, e.g. of fading and abrasion. For this reason, the threshold values for each banknote BN to be checked are individually determined on the basis of suitable reference subareas of the banknote BN in question. In this respect, in the subsequent method step S3, a plurality of suitable reference subareas are determined within the banknote BN and a plurality of upper and / or lower threshold values are determined based on their respective sections from the dark field characteristic C of the banknote BN. A reference subarea may here consist of one or more pixels, e.g. from a contiguous group of pixels of the digital image of the banknote BN, such as a local area, a column, or the like.

Therein, the upper and lower threshold values may be based on the local dark field characteristics C of different reference portions, eg by applying order operators (eg minimum, maximum, median) or distribution moments (eg mean, standard deviation) to previously determined characteristic intensity values of the local dark field characteristics C of different reference portions. At a characteristic intensity value of a local dark field characteristic C, it can For example, the intensity value of the corresponding individual pixel or else an average value, median, or the like of a plurality of pixels of the respective reference subarea.

As an alternative or in addition to determining the threshold values on the basis of the spatially resolved dark-field characteristic C of the banknote BN, the type of banknote BN can also be used for the threshold value calculation. In the simplest case, default bank thresholds for this type can be taken into account from the type of banknote BN. For example, such standard threshold values can be adapted to individual banknotes, e.g. based on the difference between characteristic intensity values (e.g., mean intensity) of the dark field characteristic C of the bill to be checked and a standard banknote. The default thresholds may then be appropriately adjusted up or down depending on this comparison to determine the respective valid thresholds for the bill to be tested BN. In this way, globally or locally valid threshold values can be determined from local standard threshold values based on suitable reference subareas of the banknote to be checked and the standard banknote for the banknote to be checked.

For example, based on the in Fig. 5 illustrated histogram analysis thresholds are determined for given reference subareas. In the histogram of the Fig. 5 the number of occurrences N of the different characteristic intensity values I of the dark-field characteristics C of given reference partial areas is plotted. In this case, the reference subregions each comprise only one pixel of the dark field characteristic C of the banknote BN, so that the characteristic intensity value I of the reference subregions corresponds exactly to the intensity value of the respective pixel. For evaluating the histogram, first the type of banknote BN is determined, which provides information about different pressure ranges of the banknote BN with different intensity distributions, eg steel pressure ranges, light pressure ranges or white field ranges. The pixels of these print areas are then selected as reference subareas and serve to determine the local threshold values for the relevant print area. The test sections to which these thresholds are applied thus correspond exactly here to the reference sections on the basis of which the threshold values were calculated.

The respective print areas are assigned the histogram sections 42a, 42b, 42c, which describe the respective expected intensity distributions. For example, e.g. the black to dark histogram area 42a is associated with the steel printing areas of the banknote and the histogram areas 42b and 42c are associated with the correspondingly brighter bright-white and white-field areas. For this assignment, in addition to the concrete intensity distribution of the individual printing areas based on the detected banknote type, also the area ratio (i.e., the number of pixels) of the respective printing area to (the total number of pixels) of the banknote BN can be consulted.

For each of the histogram areas 42a, 42b, 42c, local threshold values are then determined which are valid for exactly the relevant printing area of the banknote BN. In the present case, for example, the median value 43 is determined as the characteristic intensity value for the light-pressure range of the banknote BN based on the assigned histogram range 42b. An intensity value of an examination subarea in a light pressure range of the banknote BN which deviates significantly upwards or downwards from this characteristic intensity value (ie lies below a lower threshold or above an upper threshold) can be interpreted as an indication of counterfeiting why the subject (or pixel) in question should be assigned to a corresponding suspicious

In method step S4, examination portions 51a, 51b (cf., for example, FIG. 2) are then used for further evaluation of the electromagnetic radiation detected in step 1 Fig. 7 ) are each assigned to one of a plurality of suspect classes based on their respective dark-field characteristic C and the locally valid upper and lower threshold values previously defined in method step S3. On the basis of the suspicion classes, a distinction is made as to whether a characteristic intensity value of the respective examination section 51a, 51b lies within a range which indicates the authenticity of the banknote BN or if it lies above a first (locally valid) upper threshold which delimits the area of authenticity , lies above further (locally valid) upper threshold values, which represent particularly strong deviations from the authenticity range, or whether a characteristic intensity value of the examination subarea 51a, 51b is below corresponding (locally valid) lower threshold values. The suspicious classes thus defined thus describe the strength with which the dark-field characteristic C of the respective test sub-region 51a, 51b indicates a forgery. The characteristic intensity value of the dark field characteristic C may also be, for example, the intensity value of the corresponding individual pixel or an average value, median, or the like of a plurality of pixels of the examination portion 51a, 51b.

In principle, all possible examination subareas 51a, 51b or pixels of a suspected class can be assigned to step S4, in order subsequently to form the context area for the shape or location-based evaluation from these. For reasons of efficiency, however, suitable preliminary tests can also be carried out, for example by an intensity maximum All pixels of each column or row of the dark field characteristic C is determined and then only the pixels of those columns or rows are individually assigned to a suspicion class whose intensity maximum exceeds a predetermined threshold, since only there evidence of forgery can be expected. If a column / row thus exceeds the predetermined threshold value, the intensity values of the pixels of this column / row are compared individually with suitable local or global threshold values and then assigned to a suitable suspect class. If a column / row does not exceed the predetermined maximum threshold value, all pixels of the column / row are assigned to a suspicion class that indicates an unfalsified banknote.

In the following method step S5, essentially contiguous test subareas 51b which were previously associated with suspect classes which indicate a forgery are combined to form a context area. In the simplest case, if all examination subareas (pixels) 51a, 51b of the respective banknote BN have been assigned to a suspicion class, connection areas are formed from substantially contiguous examination subareas (pixels) 51b, which are e.g. For example, all suspicious classes that indicate a forgery have been assigned. In step S6, it is then decided on the basis of the location of such relationship areas, and possibly also on the basis of their shape, to which authenticity category the banknote BN is to be assigned. This evaluation can also be performed separately for several spectral ranges, with the separate final results, i. the determined assignments of the banknote BN to a category of authenticity, must be appropriately linked.

The criteria for establishing the area of interrelation from which examination clusters are linked with which suspect classes and when Examination subareas 51a, 51b are to be regarded as substantially coherent, are generally fixed, but may also depend on the type of the checked banknote BN and / or based on experience of previously verified banknotes, for example, from a central office (eg a central server) be updated regularly.

Likewise, as in Fig. 7 illustrates that a previously determined meaningful set of examination subareas 51a, 51b are first assigned to a suspicion class in order to search for further examination subareas 51a, 51b of the same suspicion class on the basis of this. This can relate, for example, to the examination subareas 51a, 51b lying on the edge of the banknote BN and / or in the region of a security element 25, for example enclosing the security element 25. The test portions 51a, 51b of Fig. 7 again preferably form single pixels. In this context, it is checked whether the examination subareas 51b (edge pixels) lying at the edge of the banknote BN and assigned to a suspect class suggesting a forgery can form a line-shaped or at least almost linear coherent area from further examination subareas 51b (pixels) which have also been assigned or are attributable to a suspected class suggesting a forgery. At the same time, examination subareas 51b are thereby assigned to suspicious classes and a connection area is formed, so that in the embodiment according to FIG Fig. 7 Steps S4 and S5 are combined.

In this way, a connection area in the region of a parting line 23 and / or in a region of a protruding adhesive strip 24 can be detected in a stepwise and resource-efficient manner, and from this a closed banknote BN can be deduced in step S6. Finally, in method step S6, the banknote BN is assigned to a category of authenticity. eg the category "real", "forgery", "suspected" or other categories of authenticity differentiating according to forgery probabilities.

The assignment to a category of authenticity takes place depending on the location of the ascertained relationship areas and possibly also depending on their form. In this case, a line-shaped course of a connection area from examination partial areas 51b points to a dividing line 23 of a forgery (cf. Fig. 6a, 6b ). Likewise, closed linear courses of connected areas within the banknote BN can be interpreted as dividing lines 23 of a counterfeiting (cf. Fig. 6c ), in which, for example, a genuine security element 25 was inserted into a counterfeit banknote substrate.

In addition, when assigning to a genuineness category, it is also possible to take into account the number of test subareas 51a, 51b that have been assigned to a suspicious class that indicates a forgery. In this case, the individual test subareas 51a, 51b can be weighted differently, depending on which forgery probability represents the respective suspicion class. The criteria for assigning banknote BN to certain authenticity categories, in particular the forms and locations of related areas regarded as counterfeiting, are often value-document dependent and may also be subject to a constantly updating learning process and / or provided to the authentication device 1 by a central server.

In all the described variants and embodiments of the method according to the invention, it is negligible which side of the banknote BN points in the direction of the measuring device 6. All variants and embodiments allow reliable detection of Composed banknotes and can be e.g. on personal computers as an evaluation device 11 implement.

Claims (15)

1. A method for checking the authenticity of a value document (BN),
   comprising a capturing and evaluating of electromagnetic radiation (7) passing through the value document (BN), characterized by the following steps:

   - capturing in locally resolved fashion at least one intensity distribution of the electromagnetic radiation (7) in dark field, wherein the intensity distribution is captured in the infrared region and/or in the visible spectral region and/or in the ultraviolet region, and determining a locally resolved dark field characteristic from the at least one captured intensity distribution;

   - assigning selected partial check regions (51a, 51b) of the value document (BN) to respectively one of several preset suspicion classes in dependence on a comparison of a characteristic intensity value of the dark field characteristic of the respective partial check region (51a, 51 b) with at least one upper and/or lower threshold value;

   - forming an interrelation region by aggregating substantially interrelated partial check regions (51a, 51b) which have been previously assigned to at least one certain suspicion class;

   - assigning the value document (BN) to one of at least two preset authenticity categories linked with the at least one certain suspicion class,
   in dependence on a location of the interrelation region within the value document, wherein it is checked, whether the interrelation region forms a separating line (23) extending from one side to the same side or a separating line (23) extending from one side to a different side of the value document (BN) or a separating line (23) circumferentially extending around the margin of a security element (25) of the value document (BN).
2. The method according to claim 1, characterized in that the at least one intensity distribution is captured in the infrared region and/or in the green visible spectral region.
3. The method according to claim 2, characterized in that in several spectral regions, preferably in the infrared region and in the green visible spectral region, respectively one intensity distribution is captured and the locally resolved dark field characteristic is determined from the captured intensity distributions, by mutually corresponding values of the captured intensity distributions of different spectral regions being linked with each other.
4. The method according to any of the preceding claims, characterized in that the selected partial check regions (51a, 51b) are assigned, in dependence on at least one locally valid upper and/or lower threshold value and/or at least one globally valid upper and/or lower threshold value, to respectively one suspicion class.
5. The method according to any of the preceding claims, characterized in that the at least one upper and/or lower threshold value is specified in dependence on dark field characteristics of respectively one or several partial reference regions of the value document (BN) and/or in dependence on a preset upper and/or lower standard threshold value.
6. The method according to claim 5, characterized in that for specifying the at least one upper and/or lower threshold value characteristic intensity values of the dark field characteristics of different partial reference regions of the value document (BN) are arithmetically linked with each other, preferably by averaging.
7. The method according to claim 5 or 6, characterized in that the at least one upper and/or lower threshold value is specified by an upper and/or lower standard threshold value of a standard value document being corrected upward, if a characteristic intensity value derived from the dark field characteristics of the partial reference regions lies above a corresponding standard intensity value of the standard value document, or being corrected downward, if the characteristic intensity value derived from the dark field characteristics of the partial reference regions lies below a corresponding standard intensity value of the standard value document.
8. The method according to any of the preceding claims, characterized in that
   at least one of the suspicion classes is a suspicion class indicating a forgery of the value document (BN),
   partial check regions (51b) of the value document (BN), in which the characteristic intensity value of the respective dark field characteristic lies above an upper threshold value and/or below a lower threshold value, being assigned to the suspicion class indicating a forgery, and
   of such partial check regions (51b) which have been assigned to a suspicion class indicating a forgery the interrelation region being formed.
9. The method according to any of the preceding claims, characterized in that at least one partial check region (51a, 51b) at a margin (27) of the value document (BN) or at a margin of a security element (25) of the value document (BN) is selected and assigned to a suspicion class.
10. The method according to claim 9, characterized in that there is ascertained at least one of the selected partial check regions (51a, 51b), which has been assigned to a suspicion class indicating a forgery, and starting out from this ascertained partial check region (51b) at least one partial check region (51b) substantially interrelated with the ascertained partial check region is ascertained, which also is to be assigned to a suspicion class indicating a forgery, from the ascertained, substantially interrelated partial check regions (51b) the interrelation region being formed.
11. The method according to any of the preceding claims, characterized in that the assigning of the value document (BN) to one of at least two preset authenticity categories linked with the at least one certain suspicion class is carried out in dependence on the location and in dependence on a form of the interrelation region.
12. The method according to any of the preceding claims, characterized in that depending on the number of partial check regions (51b) which have been previously assigned to at least one certain suspicion class, preferably to a suspicion class indicating a forgery, the value document (BN) is assigned to a preset authenticity category which is linked with the at least one certain suspicion class.
13. An apparatus (1) for checking the authenticity of value documents (BN), comprising a capture device (10) and an evaluation device (11) for capturing and evaluating electromagnetic radiation (7) passing through the value document (BN), characterized in that
    the capture device (10) comprises a dark field transmission measuring device (6) which is adapted to capture at least one intensity distribution of the passing electromagnetic radiation (7) in dark field in locally resolved fashion, wherein the intensity distribution is captured in the infrared region and/or in the visible spectral region and/or in the ultraviolet region; and
    the evaluation device (11) is adapted to determine a locally resolved dark field characteristic from the captured at least one intensity distribution, and the evaluation device (11) is adapted to assign selected partial check regions (51a, 51b) of the value document (BN) to respectively one of several preset suspicion classes, in dependence on a comparison of a characteristic intensity value of the dark field characteristic of the respective partial check region (51a, 51b) with at least one upper and/or lower threshold value, and
    the evaluation device (11) is adapted to form an interrelation region by aggregating substantially interrelated partial check regions (51a, 51b), which have been previously assigned to at least one certain suspicion class, to at least one interrelation region; and
    the evaluation device (11) is adapted to assign the value document (BN) to one of at least two preset authenticity categories which is linked with the at least one certain suspicion class, in dependence on a location of the interrelation region within the value document, wherein it is checked, whether the interrelation region forms a separating line (23) extending from one side to the same side or a separating line (23) extending from one side to a different side of the value document (BN) or a separating line (23) circumferentially extending around the margin of a security element (25) of the value document (BN).
14. The apparatus (1) for checking the authenticity according to claim 13, characterized in that the apparatus is adapted to carry out a method according to any of claims 2 to 12.
15. A processing device for value documents (BN), characterized by an apparatus (1) for checking the authenticity of value documents (BN) according to either of claims 13 to 14.

Images